A grid projection method has been publicly known, according to which a grid pattern is projected on an object to be measured, and a phase of each pixel of the grid pattern image that has been gained by imaging the grid pattern projected on the object to be measured is found, and thereby, the measurement of a three-dimensional form is carried out.
FIG. 1 shows an example of an optical system for an apparatus for measuring a form in accordance with a one-dimensional grid projection method.
The height of the center of the camera lens and the height of the light source of the projector are the same relative to the reference plane, and the camera imaging plane and the grid plane are in the optical system for a moire topography, which is parallel to the reference plane. In the case of this figure, the pitch of the projected grid and the pitch of the pixels that are imaged on the reference planes are the same in the position of the reference plane, and white lines can be imaged as contour lines in the W positions in FIG. 1, and black lines can be imaged as contour lines in the B positions. Even when the pitch of the pixels of the camera is smaller, the number of pixels in the pitch of the image of the projected grid is constant at any height.
In accordance with the grid projection method, phases of a grid can be analyzed so that the deformation of the grid can be analyzed with high precision, and thus, out-of-plane deformation and a three-dimensional form can be measured with high precision. A phase shift method and a Fourier transform method have been used as conventional phase analysis methods.